• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1897-1901
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• 2010

이동식 전자파표면유속계를 이용한 홍수유량의 산정을 위해서 임의의 유량측정지점에서 측정한 표면유속 값에 수심평균유속환산계수 0.85를 적용하여 그 지점의 평균유속을 계산하고 있다. 이로 인해 각 지점에서 흐름조건 및 기상학적으로 요인으로 인한 이 계수의 변동성을 고려하지 않은 상태로 유량을 산정하게 되어 각 흐름조건을 고려한 유량산정을 할 수 없는 실정이다. 이에 하천 현장에서 표면유속과 수심별유속의 실측 자료를 이용하여 흐름조건에 따른 표면유속과 평균유속의 관계를 파악하고자 하였다. 이를 위하여 용담 수자원시험유역의 동향지점에서 하천을 횡단하며 바닥에서 수표면까지 수심방향으로 0.05~0.10 m의 간격으로 프로펠러 유속계를 이용하여 정밀법으로 각 수심에서의 유속을 측정하였다. 정밀측정된 수심별 유속을 이용하여 평균유속을 산정하고 이를 수체 (water column)의 가장 최상층에서 측정한 유속을 표면유속으로 가정한후 이로부터 수심평균유속환산계수를 산정하여 흐름조건에 따른 계수의 변화를 조사하였다. 하천 현장에서 흐름조건의 변화에 따른 표면유속과 수심별유속의 정밀측정을 통한 이들 깊이별 유속의 변화여부를 용담수자원시험유역의 동향지점에서 현장조사를 실시하였다. 측정당시 풍속이 느려서 (1.5~3.1 m/s) 바람으로 인한 유속에 미치는 영향이 수심별 유속분포상으로는 거의 나타나지 않았다. 다만 양안에서 평균유속과 표면유속이 역전되는 현상이 발생되었는데 이는 벽면 마찰에 바닥마찰의 영향이 추가됨에 따른 것으로 판단된다. 수심별 유속측정 결과를 전체적으로 분석한 결과 환산계수가 0.632~1.352로 넓게 분포하고 있다. 환산계수가 1.0 이상인 경우는 양안에 인접한 두 지점인데, 이들 두 경우는 유속분포가 이론적인 유속분포와는 상반된 유속이 측정 - 표면유속이 수심평균유속보다 느림 - 되었다. 환산계수가 0.6~0.8 사이에서 형성된 경우는 표면유속이 평균유속보다 25~55% 정도 빠르게 나타나고 있다. 전제 측정결과를 검토해보면, 전반적으로 양안에 인접한 측선에서 표면유속이 평균유속보다 느려지는 현상이 나타나고 있다. 또한 유속이 1.0 m/s 이상인 경우에 0.677~0.790의 환산계수 값을 보이는데 이 경우 수심이 50 cm 이하여서 바닥마찰의 영향이 큰 것으로 판단된다. 다양한 흐름조건별 표면유속과 수심별유속의 측정을 할 수 있는 현장여건 - 유속, 수위 등의 동일흐름 조건에 대해서 -에 많은 부분이 제약되어 이의 정밀분석이 힘든 실정이다. 따라서 이러한 현장측정시의 제약성을 극복하기 위해서 여러 가지 흐름조건을 구현할 수 있는 정밀제어가 가능한 실내실험장치를 이용한 면밀한 분석이 필요하다.

• Tunnel and Underground Space
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• v.32 no.5
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• pp.312-326
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• 2022

The generalized Hoek-Brown (GHB) criterion, which is recognized as one of the standard failure conditions for rock mass, is specialized for rock engineering applications and covers a wide range of rock mass conditions. Accordingly, many research efforts have been devoted to the incorporation of this criterion into the stability analysis of rock structures. In this study, the slip-line analysis method, which is a kind of elastoplastic analysis method, is combined with the GHB failure criterion to derive analytical equations that can easily calculate the plastic radius and stress distribution in the vicinity of the circular tunnel. In the process of derivation of related formulas, it is assumed that the behavior of rock mass after failure is perfectly plastic and the in-situ stress condition is hydrostatic. In the formulation, it is revealed that the plastic radius can be calculated analytically using the two respective tangential friction angles corresponding to the stress conditions at tunnel wall and elastic-plastic boundary. It is also shown that the plastic radius and stress distribution calculated using the derived analytical equations coincide with the results of Lee & Pietruszczak's numerical method published in 2008. In the latter part of this paper, the influence of the quality of the rock mass on the size of the plastic zone, the stress distribution, and the change of the tangential friction angle was investigated using the derived analytical equations.

• Journal of the Korean Geotechnical Society
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• v.27 no.3
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• pp.41-54
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• 2011

The present study analyzes the stability of waterfront quay wall under the combined action of earthquake and tsunami. Adopting the limit equilibrium method, the stability of waterfront quay wall is checked for both the sliding and overturning. Forces due to tsunami are compared with the proposed formula and the 3-D one-field Model for immiscible TWO-Phase flows (TWOPM-3D). Variations of the stability of wall are also proposed by the parametric study including tsunami water height, horizontal seismic acceleration coefficient, internal friction angle of soil, friction angle between the wall and the soil and the pore water pressure ratio. The present study about the stability of wall is also compared with the case when earthquake and tsunami are not considered. As a result, the result of numerical analysis about the tsunami force is similar to that of proposed formula. When earthquake and tsunami are simultaneously considered, the stability of wall in passive case significantly decreases and tsunami forces in active case are affected as a resistance force on the wall and so the stability of wall increases.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.167-176
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• 2004

Underground structures will be affected by the additional surcharge loads such as traffic load et al. Terzaghi (1956) suggested the equation on the influences of surcharge loads in vertically backfilled spaces. In field, the shapes of backfill spaces are not always formed vertically. Then the Terzagi (1956) equation is not suitable to use because of boundary condition. This study suggests equation to calculate the stress in backfilled space caused by surcharge loads when the backfilled space is sloped symmetrically. The suggested equation is verified by carbon box test and numerical analysis. The experimental results show good agreement with the suggested equation but the numerical analysis result shows a little disagreement. The differences are estimated to be caused by the fact that ground made by carbon rod has become more dense and internal frction and wall friction has increased itself as surcharge load is added but that this increase can not be considered in the numerical analysis. The suggested equation shows good agreement with Terzaghi (1956) equation in case of sloped backfill ground. According to the results, it is considered that the suggested equation can be applied not only to sloped space but also to vertical space. Further investigation using full scale experiment is needed.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.51-60
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• 2020

Estimation of passive earth pressure is an important factor in anchor block, temporary retaining wall and support block of raker that resist lateral earth pressure. In practice, due to ease of use, it is common to estimate the earth pressure using the theory of Coulomb and Rankine, which assumes the failure plane as a straight line. However, the passive failure plane generated by friction between the wall surface and the soil forms a complex failure plane: a curve near the wall and a flat plane near the ground surface. In addition, the limit displacement where passive earth pressure is generated is larger compared to where the active earth pressure is generated. Thus, it is essential to calculate the passive earth pressure that occurs at the allowable displacement range in order to apply the passive earth pressure to the design for structural stability reasons. This study analyzed the mobilized passive earth pressured to various displacement ranges within the passive limit displacement range using the semi-empirical method considering the complex failure plane.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.650-655
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• 2016

In this study, a computational simulation of the internal flow characteristics was carried out for a Urea-SCR Injector. A single hole swirl injector with a swirl disk and slanted nozzle was used in this simulation. The maximum needle lift and opening velocity were selected as the design parameters. To analyze the unsteady internal flow characteristics of the Urea-SCR injector, the moving grid technique was applied to simulate the delicate needle movement. According to the simulation results, the injected mass flow rate from the Urea-SCR injector decreased with increasing needle opening velocity and maximum needle lift. This is because the Urea-solution tends to fill the empty space that the needle previously occupied. The swirl flow is decreased as the flow goes through the injector nozzle, because of the friction with the nozzle wall. Also, during the maximum needle lift period, the swirl coefficient and mean swirl coefficient increase with increasing needle lift. The results of this study may be used as the basic design data of related injectors.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.1-8
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• 2014

Two-dimensional laminar numerical analyses were carried out for investigating the thermo-hydraulic characteristics of wavy channels with different shape parameters ($0.5{\leq}{\in}{\leq}1.5$, $0.1{\leq}{\gamma}{\leq}0.4$). PAO (polyalphaolefin), which is used for electronics cooling, is considered as the working fluid. In addition, constant properties, periodically developed flow, and uniform channel wall temperature conditions are assumed. Streamline and temperature fields, isothermal Fanning friction factors, and Colburn factors are presented for different Reynolds numbers in the laminar region ($1{\leq}Re{\leq}1000$). The results show that heat transfer is enhanced when the channel corrugation ratio (${\gamma}$) is large and channel spacing ratio (${\in}$) is small in the low Reynolds number region (Re < 50) and when ${\in}$ and ${\gamma}$ are large in the high Reynolds number region ($Re{\geq}50$).

• Journal of the Korean Geotechnical Society
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• v.30 no.9
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• pp.5-17
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• 2014

A series of model tests were conducted in order to observe the failure surface generated around a diaphragm wall embedded in ground with high groundwater table. Images of the soil deformation around the model wall were captured during the test. The configuration of the failure surface in soil around the model wall could be obtained from analyzing the image of the soil deformation. Based on the configuration of the failure surface observed in the model test, an analytical approach was proposed to predict the uplift capacity of a diaphragm wall installed in ground. The analytical approach considers not only the wall properties such as length, thickness and surface roughness of diaphragm walls but also the soil strength properties such as the internal friction angle and the cohesion of soil. The predicted uplift capacity of a diaphragm wall shows a good agreement with the experimental one measured in the model test.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.49-62
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• 2007

A new earth pressure equation acting on the vertical shafts in cohesionless soils has been proposed by modifying the equations proposed by others. In order to verify the modified equation, model tests which can control uniform wall displacement with depth to radial direction were conducted. Model tests were performed with three different wall friction angles and two different relative densities. The measured values were larger than estimated values when assuming $\lambda=1$ ; smaller than those when assuming $\lambda=1-sin\phi$. The parameter, $\lambda$ is the ratio of tangential stress to vertical stress and is the most critical value in proposed equation. A method which can estimate the earth pressure on vertical shafts in layered soils is also proposed by reasonably assuming the failure surface of layered soils and using the modified equation. In order to verify the proposed method, in-situ measurement data have been collected from the three in-situ vertical shafts installed in layered soils. Most of earth pressures converted from measured data match reasonably well with estimated values using proposed method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.10
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• pp.773-778
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• 2015

The local heat transfer and pressure drop of developed turbulent flows in convergent/divergent channels with square axial cross-sectional areas were experimentally investigated to improve the channel design, such as a gas turbine cooling system. Square convergent/divergent channels with one ribbed wall were manufactured with a fixed rib height e of 10 mm and a ratio of rib spacing p to height e of 10. The measurement was conducted for Reynolds numbers from 15,000 to 89,000. Convergent, divergent, and straight channels with ratios $D_{ho}/D_{hi}$ of 0.75, 1.33, and 1.0, respectively, are considered. Of the three channel types, the ribbed divergent channel was found to produce the best thermal performance under identical flow rate, pumping power, and pressure loss conditions.